Night switching for private automatic branch exchanges



G. DEAKIN Aug. 29, 1950 NIGHT SWITCHING FOR PRIVATE AUTOMATIC BRANCH EXCHANGES Original Filed May 14, 1945 7 Sheets-Sheet 1 FIG.\

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NIGHT SWITCHING FOR PRIVATE AUTOMATIC BRANCH EXCHANGES miginal Filed y 14, 1945 l 7 Sheets-Sheet e INVENTOR.. @5844 a f'fiK/A/ KGENT Au 29, 1950 DEAKIN NIGHT SWITCHING FOR PRIVATE AUTOMATIC BRANCH EXCHANGES Original Filed May. 14, 1945 '7 Sheets-Sheet '7 AGENT Patented Aug. 29, 1950 NIGHT SWITCHING FOR PRIVATE AUTO- MA'IIC BRANCH EXCHANGES Gerald Deakin, New York,. N. Y., assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Original application May 14,, 1945, Serial No. 593,602. Divided and this; application May21, 1945, Serial No. 594,872

8 Claims. (Cl. 179-27) This invention relates to new and useful improvements in automatic telephone systems, and more particularly to improvements applicable to small. telephone exchanges.

The object of the present invention is to provide for so-called night switching service whereby calls coming into an exchange when the customary attendant is absent may be. routed direct to one of the subscribers stations- The present is a division of my copending application, Serial, No. 593,602, filed May 14,, v19451.

The various features of the invention will more readily appear from the following description of an embodiment thereof as applied to. the drawings, in. which:

Figs. 1, 2 and 3 illustrate diagrammatically an inter-exchange trunk and the attendants position;

Figs. 4,411, and. 4b illustrate a local link and the line finder and the selector by which it may be extended to an inter-exchange trunk or a called. station;

Fig. 5; illustrates. the nightswitchinglink; and

Fig, 6 illustrates themanner in which the drawings should. be combined.

Only so. much is disclosed herein as is. necessary for an understanding of the invention.

During the night or hours of light trazfficwhen the attendants position is shut down all or a portion of the P. A. B. X'trunks may be converted to automatic i-n-trun-k switching to a predetermined P. A. B. X station by throwing the night switching key which forms part of each trunk. For. this direct switching service individual numbers are assigned to the trunks and. listed in the telephone directory as night numbers. The lamps on the attendants switchboard operate substantially as usual so that 'all calls may, when desired, besupervised. Nolamp remains burning when the calling city party hangs up and frees the trunk; I

When a trunk converted for night switching is selected at the central oflice, it is automatically picked up at the P. A. B; X by a special night switching link" (Fig. 5)" which, without using the P. A. B. X register, controls the selectors automatically to extend the trunk call to the- P. A. B. X station assigned to night service.

The city cal-lisnot metered. until the P. A. B. X station answers. If the trunk is busy at the central office, the city subscriber receives the usual busy tone:- but tithe. trunk is free, the city subscriber receivesz the usual ringing tone. This ringing tone will: continue until the P. A. B; X station answers or until the calling station lamp caps. may be given special colors or the trunks otherwise identified so that the attendants may know that such calls will be extended automatically.

The P. A. B. X stations assigned for automatic selectionmay be called over other trunks through the attendants position in the usual way. Such stations may make local, outgoing trunk, information, transfer and flash-in calls in the usual way. In; other words, assigning a station to a trunk does not restrict its. customary use. Assigned as well as unassigned P. A. B. X stations may pick upany-trunk when making out-trunk calls. When, therefore, the night keys are thrown, all the trunks remain available to all the stations for out-trunking.

The B-l'i-nk finders of the night switching links Fig. 5) are like those provided for the R-links. Their terminal banks have a capacity for B-li-nks. The number of night switching links required depends upon the number of automatic switching calls to be handled simultaneously. Usually two or three NS-links will be sufficient fora large P. A. B. X.

Referring now to the specific means for performing the above-described functions:

Night switching key NSK thrown To convert a trunk for automatic in -switching service, it is only necessary to throw the night switching key NS-K (Fig. 1). When this key is thrown, ground is placed upon the filaments of the tubes Vl-Vfi in the night switching circuit (Fig. 5). These triodes and their associated gas valves GVP, GVZ' and relays function in the same manner as the corresponding equipment described in connection with the register. The tubes burn only when a night switching key is thrown.

The night switching key has one contact to place a distinctive calling potential P04 on, a front contact of BB (Fig. 1). Over a second contact the keyconects terminals T of the B- link finder 'banks of the night switching links (Fig.5; to another front contact of BB;- (Fig. 1),.

3 To the same T-terminal is connected through resistor R2 a starting relay GSR which is common to all trunks appearing in a given quadrant of the link finder banks. should the trunks be distributed over all quadrants, there would be four GSR relays.

Trunk selected at central oflice When a trunk is selected at the central oflice, ringing current is applied to it in the usual way and AR (Fig. 1) operates to energize BR. BR locks up over a back contact of HR, and the contact of TA. BR places calling potential PC4 on the T-terminal (Fig. 2) of the trunk. This will insure the selection of the trunk only by the line finder of a B-link connected with an NS-link, since PC4 is normally connected over CR2 back (Fig. to the grids of VI and V3.

BR also places battery on terminal T of the NS-link (Fig. 5) through resistor RI and energizes through resistor R2, GSR (Fig. 1). GSR places battery on the common starting lead Zl to the starting circuit (Fig. 4a), thus making it possible for the NS-link (Fig. 5) to select a'first choice B-link (Fig. 4a).

NS-link picks up B-Zinle GSR (Fig. 1) places ground on common lead X to all the NS-links (Fig. 5) and energizes FR in each link over a back contact of T4R. FR energizes the associated B-link finder magnet Pl over back contacts of TIR and T4R and at the same time places ground on the high resist- .ance winding of TIR.

The NS-links hunt for an idle B-link in the same manner as R-links hunt for an idle B-link on a regular call.

When a B-link is picked up, TIR operates and shunts its high resistance winding by its low resistance winding in series with TZR, thus making the selected B-link busy.

NS-Zink picks up trunk T2R (Fig. 5) closes the circuit of the trunk and translator finder' magnet P2 and places groundon the high resistance winding of T3R. The trunk and translator finder is like the customary register finder. However, its wiper T hunts for the city trunk, and its wipers A, B, C for potentials connected in combinations determined by the number of the station to which such calls are channelled.

When wiper T reaches the calling trunk T3R operates over a circuit from ground, front T2R, high resistance winding T3R, brush T, resistor RI (Fig. 1) of the trunk, NSK, front BR to battery. T3R (Fig. 5) operates, energizes T4R, disconnects P2 and makes the selected trunk busy.

The low resistance test circuit thus established shunts out GSR (Fig. 1) which releases and causes any other hunting NS-links to come to rest. GSR also removes battery. from the Zllead to the starting circuit.

T4R (Fig. 5) disconnects the X-lead running from GSR (Fig. l) to FR (Fig. 5) but before doing so, closes a circuit for FR to ground and over another front contact. T3R closes a holding and busying test circuit through T3R and T4R. T4R opens the circuit of PI, thus preventing its re-energization when TIR and T2R fall oil.

B-linlc selects trunk circuit from the a wire of the B-link (Fig. 4a) brush A of the B-link finder, front DR, back CR2, back AR, back GSRI, back GVRI to ground. The circuit of the "b wire is closed from the B-terminal, front DR, back CR2 to the grids of triodes V2 and V4.

The line finder in which the B-link terminates hunts for the city trunk in substantially the same manner as any other B-link under the control of a register hunts on a regular call for a calling line.. The only difference is that the line finder of the B-link is now hunting for the potential PC4 placed on the T-terminal of the trunk over key NSK (Fig. 1) and a front contact of BR. Since the grids of VI (Fig. 5) and V3 are connected to the same PC4 potential over a back contact of CR2, when the calling trunk is found, GVI fires in the usual manner and energizes GVRI which removes ground from the a wire and causes the line finder to come to rest on the city trunk.

Second test at line finder GVRI energizes GR, GR energizes GSRI and places high tension battery on the second group of electronic discharge devices including GV2, V3 and V4.

GSRI energizes QR which looks up over a back contact of GVR2 and front DR. When high tension battery is placed on V3 and V4, a second test is made in the same manner as in the register from the grid of V4, over CR2 back, DR front, the b wire, the B-terminal of the trunk (Fig. 2), back contacts of COR, JR (Fig. l) and HR, BR front, NSK to PC4. GV2 fires and energizes GVR2.

GVR2 releases QR and over a front contact energizes CRI.

GSRI opens the high tension battery to GVI which GVI de-ionizes and releases GVRI releasing GR and, in turn, GSRI. As GSRI is somewhat slow releasing, it maintains open the fundamental circuit so that ground is not again immediately placed on the "a wire. When GR breaks its front contact it de-ionizes GV2, releasing GVR2 which removes the short-circuit from CR2. CRI locks up in series with CR2,

circuit from ground, front DR, winding CR2,

front CRI, winding CRI to battery.

Group selector selects final We shall assume that the station assigned to answer calls on the trunk has the number 342.

When CR2 makes its front contact, it grounds the a wire of the first group selector (Fig. 4a) over brush F (Fig. 5) front DR, back BR, front CR2, back AR, back GSRI back GVRI to ground.

Potential PN3 corresponding to the first digit of the wanted number is placed on the grids of VI and V3 over a resistance rt, terminal and brush C of the trunk and translator finder, back CR4, front CR2 to grids VI and V3.

The group Selector selects an idle final (Fig. 4b) in the usual way after which a second test is made, again in the usual way and when successful GVR2 operates for the second time and energizes CR3 over a front contact of CR2.

Final selects "tens When GVR2 falls away for the second time, CR4 locks up in series with CR3 and the fundamental circuit is again closed. This time potential BN4, corresponding to the second digit, is placed on the grids of VI and V3 over brush B of the trunk and translator finder, back CR6,

tact-s CR6, CR4 and CR2.

5. front CR and front CR2. The .tens is selected in the usual way after which the usual second test is made.

Final selects units When GVR2 operates for the third time, CR operates and whenit releases CR5 locks upin series with CR6 and the fundamental circuit-is closed for the third and last time. Potential PNZ, corresponding to the last digit of the number, is placed on the grids of VI and V3 over wiper A of the translator finder, and front con- When the called line is reached GVRI operates and the final comes to rest on the terminals of the assigned station. I

Called station free If the called station is free, GVR2. operates for the fourth time and energizes FRI, circuit from ground, front DR, front GVR2 front CR2, front CR4, front CR6, winding FRI to battery. FRI energizes BR which looks up to ground over a. front contact of DR. BR connects the a wire of the called line over brush F to ringing current source through RRR, and over. the G- brush, the 2) wire of the line to ground. FRI supplies over a front contact an immediate ring. When GVRZ breaks its front contact and FRI makes its back contact, ringing current is supplied over the usual ringing interrupter RI. The city subscriber receives the central ofiice ringing tone.

Called station answers When the station answers, marginal ringing relay RRR (Fig. 5) breaks itsback'contact and releases 'DR- which disconnects the ringing current from the called line.

DR also releases BR but as BR is slightly slow releasing, a momentary circuit is established from negative battery, front BR, back DR, brush D and the B-link (Fig. 4a), thence to the T- terminal of the trunk (Fig. 2), front COR, back ER, front DR, rectifier S5, winding CR to ground.

Trunk connected through to the called station CR (Fig. 2) .energizes and bridges the low resistance high impedance relay TR (Fig. 1) across the trunk, thereby tripping theringing relay (not shown) at the central oflice and completing the call at that end.

TR removes ground from the holding circuit of ER (Fig. 1). BR releases and removes battery from the T-brush of the trunk and translator finder (Fig. 5), thus releasing relays T3R and T lR which release FR. The night switching link is now entirely freed.

CR (Fig. 2) bridges the supervisory relays SIR and 32R across the A and B terminals of the trunk. At the same time CR effectively shortcircuits the high resistance winding of COR, thereby causing CRI (Fig. 4a) of the B-link to operate and energize ER, which removes the local transmission bridge from the B-link. The answering station now receives transmitter current from the bridge in the trunk circuit over a clean pair of wires through the B-link and final.

Release The release of the trunk is accomplished in the same manner as on trunk calls established via the attendant.

Called station busy Should the called station be busy, GVRZ (Fig. 5) will not operate. Therefore, when GSRI makes: its. back contacha' circuit. will be .estah lished from ground, back GSRI, front QR, winding'ARto battery andin multiple over, a back contact. :of winding .ER to battery. .ER.-.-i s disconnected by ARbut .operateslong enough to place negative battery on brush .E, thereby momentarily. operatinaFRZ (Fi 4 of the B- link which releases the final and group selector as one normalbusy call.

.AR (Fig.5) bridges the primary winding of busy tone transformer. TT, the center point of which-is grounded, across the av and b wires ofrthe trunk to thecentral ofiice.

Condenser Qprevents the flowof. current to the b wire but ground on the a wire trips theringingrelayv at the central office (Fig- 1) and thereby. connects. the calling city subscriber :to. the trunk. The calling. subscriber hears the busy 'tonepbut the .meteri not operated since the 1; wire is not grounded.

Release Ordinarily the calling subscriber hangs up promptly when he hears the busy-tone. However, should he not hang up promptly, the busy tone will cease within a maximum of five seconds since removal of ringing current from the trunk de-energizes AR (Fig. 1) thus permanently closing the circuit of 'TA over the front contact of BR. -In five seconds or so, TA opens the looking circuit or 'BR. "BR releases, disconnects TA and removes battery from the T-terminal of the trunk and translator finder which releases T3R (Fig. 5), T4R and FR.

'T iR releases DR. "DR opens the locking circuit of QR and this in turn de-energizes' slow releasing relay ARQ However, before AR releases, DR applies ground over its back contact and a front contact of 'AR to energize slow releasing relay'ER. ER places battery on the E-brush of the-B-link andagain energizes FR2 (Fig. 4a).

Since both AR (Fig.5) and ER are slow releasing, the circuit of-FRZ (Fig. 4a) is'held closed-long enough to allow RR to de-e'nergize and break its front contact to release the B-link.

The B-link and the NS-link are now restored to normal. s

Should the calling subscriber fail to hang up after the busy tone ceases, the trunk is held busy at the central ofi'ice by the final and at the P. A. B. X by energization of the high resistance relay JR (Fig. 1) which opens the t wire circuit, thus preventing the trunk from being picked up by a B-link at the P. A. B. X. The energizing circuit of JR may be traced from ground, one winding of DR or SR of the central office (Fig. 1), "a wire, back LR, back BR, back COR (Fig. 2), rectifier SI, (Fig. 1), winding JR, "b wire, other winding of DR or SR to battery. When the calling subscriber finally hangs up, the condition at the central oflice changes from that indicated at TD (Fig. 1) to that indicated at N. With this reversal of polarity, no current flows through rectifier SI and JR releases.

What I claim is:

'1. In a telephone system, an exchange having a plurality of stations and outside trunks, an attendants position, a plurality of automatic switches, means controlled by the attendant for answering an incoming trunk call and for operating said switches to connect the calling trunk with a called station, a night switching key for each trunk, a night switching link circuit means operable when the night switching key associated with a trunk is operated and responsive to a call incoming thereonfor operating said night switching link circuit to find the calling trunk, and means controlled by said night switching link circuit for causing certain of the automatic switches to extend the trunk to a predetermined station.

2. In a telephone system, the combination as defined in claim 1, in which the exchange includes local link circuits and the means for causing certain of the automatic switches to extend the trunk to a predetermined station comprises one of the local link circuits, means for causing the night switching link circuit to seize said local link circuit, and means for causing said local link circuit to seize said trunk.

3. In a telephone system, the combination as defined in claim 2, in which the automatic switches are both numerical and non-numerical and in which the night switching-link circuit is provided with numerical switch control equipment which controls the numerical switches in the local link circuit for connecting the trunk to the predetermined station. 4. In a telephone system, the combination according to claim 3, in which means is provided in the night switching link for successively connecting the numerical control equipment to successive stages of selectors.

5. In a telephone system, the combination according to claim 3, in which the numerical control equipment of the night switching link circuit is preset to control predetermined selecting operations to reach a certain station over the selectors.

6. In a telephone system, the combination according to claim 3, in which a plurality of different sources of potentials are connected with the night switching link circuit, means in each selector for connecting the different potentials with the night switching link circuit, the numerical control equipment in the night switching link circuit comprising means for starting said selectors one after the other and for stopping each selector when the potential connected by it bears a predetermined relationship to a certain one of said potentials. I

7. In a telephone system, a private branch exchange having a plurality of Stations and. outside trunks, an attendants position, automatic nonnumerical and numerical switches at the private branch exchange, means including at least a numerical switch controlled by the attendant for connecting a calling trunk with the desired called station, a night switching key for each trunk, a night switching link circuit means operable when the night switching key associated with a trunk is operated and responsive to a call incoming thereon for operating said night switching link circuit to find the calling trunk, and means controlled by said night switching link circuit for causing a non-numerical and at least one numerical switch to extend the trunk towards a predetermined station.

8. In a telephone system, a private branch exchange having a plurality of stations and outside trunks, an attendants position, automatic selector and line finder switches at the private branch exchange, means controlled by the attendant for answering an incoming trunk call .and for operating a line finder to connect the calling trunk with a selector and the selector for extending the call towards the called station, a night switching key for each trunk, a night switching link circuit, a line finder connected thereto, means operable when the night switching key associated with a trunk is operated and responsive to a call incoming thereon for causing said night switching link circuit to find the calling trunk, and means controlled by said night switching link circuit for causing a line finder to select the calling trunk and a selector to extend the calling trunk via the last mentioned line finder towards a predetermined station.

GERALD DEAKIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,668,541 Schwartz May 1, 1928 1,693,599 Gillings Dec. 4, 1928 2,214,914 Voss Sept. 17, '1940 2,335,481 Boswau Nov. 30, 1943 2,380,950 Deakin Aug. 7, 1945 

